Electric shaver cutter assembly

ABSTRACT

A dry shaver having a cutter with a shank part movable in a holder axially and slightly inclinable, and a blade part of the cutter urged against a shear plate by a spring, the shank, when inclined due to cutting action, having axially spaced parts thereof engaging the holder which locks the cutter&#39;&#39;s position from further axial or tiltable movement.

United States Patent Tietjens v 1 Jan. 25, 1972 [54] ELECTRIC SHAVER CUTTER [56] References Cited ASSEMBLY UNITED STATES PATENTS [72] Invent Eduard Drachtem 2,520,487 8/1950 Arey ..30 43.a

Netherlands [73] Assignee: U.S. Philips Corporation, New York, NY. i y Examiner-Andrew hil- Z Assistant ExaminerGary L. Smith [22] July 1969 AnomeyFrank R. Trifari [2]] Appl. No.: 841,237

[57] ABSTRACT [30] F i A li i priority Data A dry shaver having a cutter with a shank part movable in a holder axially and slightly inclinablc. and a blade part of the July 19, I968 Netherlands ..68 10337 cutter urged in t a shear plate by a Spring, the shank. when inclined due to cutting action, having axially spaced parts [52] US. Cl ..30/43.6, 30/3465] h f engaging the holder which locks he cuner's posmoh [51 Int. Cl ..B26b 19/14 f f th axial or tihable movement [58] Field of Search ..30/43, 43.2, 43.3, 43.9, 43.91,

30/43.92, 32, 42, 43.6, 346.5] 6 Claims, 7 Drawing Figures AXIS 0F 17074770 01'' C U7 7' 1? l/OL 5R CASING 0 ELECTRIC SHAVER CUTTER ASSEMBLY The invention relates to a hair-cutting device, particularly a dry shaver, having within its housing a shear plate and a cutting member which cooperates with the shear plate and is adapted to be driven and consists of a holder having at least one cutter, the cutting edge of which is movable over the surface of the shear plate facing the cutting member. The shear plate is provided with at least one aperture for the passage of hairs through which the hairs to be cut extend during the cutting operation. A portion of the shank of the cutter more remote from the cutting edge is accommodated for part of its length in the holder which is adapted to be driven by a motor or other drive means and is spaced from the shear plate and is movable in a direction parallel to the shear plate.

In the construction of such a known device, care must be taken to ensure as much as possible during the cutting action of the device that the cutter and the shear plate remain in close engagement, because the entire cutting process takes place in the plane of engagement between the cutter and the shear plate. With a departure from this desired engagement, the movable cutter tends to slide over the hairs to be cut, and at most to scrape them off, which gives rise to the so-called pulling. it should be added that the thrust force to be used for urging the movable cutter against the shear plate to obtain the desired engagement is considerably increased, if the usual unevennesses of the cooperating parts is to be taken into account. Anyhow the frictional resistance between the cutter and the shear plate to be overcome during the operation of such a known device, may increase to a value such that a source of energy is required which is very powerful in relation to the cutting force for cutting the hairs, and this is objectionable with respect to the cost of manufacture, the bulk of the device, handling the device in view of possible running hot of the component parts, and so on.

It is an object of the invention to avoid or reduce these disadvantages; and the invention is characterized in the inoperative condition of the device, or at no-load during the operation of the device, that the portion of the cutter accommodated in the holder is fittingly movable in an aperture of prismatic design having an arbitrarily shaped base which is provided in the holder. The generatrix or axis of this aperture extends towards the shear plate, preferably at right angles thereto, while during the cutting action of the device the holder and the cutter are clampingly coupled in the direction of the axis owing to the forces produced by the cutting action and applied to the cutter.

A preferred embodiment of the device according to the invention is characterized in that the cutter cooperates with a spring which exerts a force on the cutter, which force acts in a direction along the axis of the aperture in the holder towards the shear plate, and is slightly greater than the force exerted on the cutter by gravitation. The thrust force exerted by the spring ensures that in any orientation of the device in the nonoperative condition, the cutting edge of the cutter remains in engagement with the shear plate.

At the commencement of the cutting action of the device according to the invention, a resultant of reaction forces produced by hairs to be cut, which resultant acts on the cutting edge in the plane of engagement, will clampingly couple or locked together the holder and the cutter.

This clamping coupling or junction manifests itself in the form of frictional forces between the holder and the cutter. These frictional forces, which act on the shank of the cutter, are directed towards the cutting edge of the cutter and eliminate the other resultant of the aforementioned reaction forces, which resultant is directed away from the shear plate and acts on the cutting edge of the cutter, with the result that the cutter remains fixed in the situation in which it engages the shear plate. The magnitude of the forces directed towards the cutting edge matches the magnitude of the forces directed away from the cutting edge. A similar matching of these forces takes place in the no-load condition during the operation of the device.

The cutter can freely reciprocate in the holder against the spring pressure when the holder begins to move, in the absence of obstacles such thatthe cutting edge of the cutter will travel smoothly over the shear plate and will be able to follow all the unevennesses. At no-load during the operation of the device, small frictional forces are produced by the sliding contact of the cutting edge of the cutter, which forces ensure a certain amount of damping. If for any reason the cutting edge of the cutter should nevertheless get out of engagement with the shear plate, the cutting edge will rapidly and undampedly return to its engagement with the shear plate.

During the cutting action of the device the cutting edge of the cutter remains fixed in its engagement with the shear plate, while during a possible subsequent no-load condition of the device the substantially frictionless contact between the cutting edge of the cutter and the shear plate is restored, since the cutter with respect to the shear plate passes again from its fixed situation to a flexible situation.

Features and advantages of the invention will appear from the following description of embodiments thereof, given by way of example only, with reference to the accompanying drawings in which:

FIG. 1 shows schematically the reaction forces exerted on the cutting edge of the cutter at the commencement of a cutting action,

FIG. 2 shows schematically an embodiment;

FIG. 3 shows schematically an embodiment similar to that shown in FIG. 2, in which, however, a cutter engages the shear plate under spring pressure;

FIG. 4 shows schematically an embodiment as shown in FIG. 2, in which part of the shank of the cutter is shaped in the form of a hook; and

FIG. 5 is a schematic representation of the forces produced by the cutting process in the embodiment shown in FIG. 3,

FIG. 6 is a fragmentary view in section of the invention with the blade shown in an exaggerated inclination and locked in place, and

FIG. 6a shows a force diagram of the blade in FIG. 6.

Referring to FIG. 1, there is shown a hair 2 which is to be cut by a stationary shear plate 1 and engages a cutting edge 3 of the shear plate 1 and is about to be cut by a cutting edge 4 of a movable cutter 5 (which is moving to the left). At this instant of the commencement of cutting, there is produced a reaction force R which originates from the hair 2 to be cut and acts on the cutting edge 4 of the moving cutter 5 and can be resolved into two components K and S, K being perpendicularly directed from the shear plate 1 onto the cutter 5. and S being directed parallel to the shear plate 1 but opposite to the direction of movement of the cutter 5. The vector K indicates the magnitude of the thrust force required to prevent the cutter 5 from being lifted and the vector S shows the cutting force required to cut the hair 2.

In the ideal case, the cutting edge 4 of the moving cutter 5 glides over the shear plate 1 with zero spacing so that. perfect engagement between the cutting edges of the cooperating cutters is obtained. In practice, however, this spacing x has a POSI? tive value owing to various tolerances.

In order to permit cutting action, the cutting edges of the cooperating cutters must not move apart during the cutting operation of the device. For this purpose, in order to prevent the cutting edge 4 of the moving cutter 5 from being lifted and gliding over the hairs to be cut, the cutting edge 4 of the cutter 5 will have to be urged into engagement with the shear plate I with a force at least equal in magnitude to K. For the known devices this magnitude of the thrust force must be present not only during the cutting operation of the device, but also at noload operation of the device; and consequently during this noload condition the cooperating cutters move over one another with excessive friction. It is the object of the invention to eliminate this actually needless urging together of the cutters.

The surprising solution of this problem will now be described with reference to FIG. 2. A cutting member 7 comprises a holder 8 carrying at least one cutter 5. The holder 8 moves parallel to the shear plate I. The holder 8 is provided with a prismatic aperture 9 in the form of a slot in which an upper portion 10 of the shank of the cutter 5 is fittingly movable. When the holder 8 of the cutting member 7 begins to move, the cutting edge 4 of the cutter 5 will (in the absence of obstacles) be caused, for example, by its own weight or, in the case of a holder adapted to be rotatably driven, to run smoothly over the shear plate and will be able to follow any unevennesses. This results in a satisfactory engagement of the cutting edges of the cooperating cutters, while in a possible no-load condition during the operation of the device these cutting edges move over one another substantially without friction. When the cutting edge 4 of the cutter 5 meets a hair to be cut which protrudes through the shear plate 1, owing to reaction forces Fr produced the said upper portion of the shank of the cutter will be clampingly coupled to the holder 8, and will remain fixed in this position during the cutting action of the device.

FIG. 3 shows schematically an embodiment in which the cutter 5 is thrust with a small force against the shear plate I by means of a spring 11. The cutter 5 is, however, capable of free reciprocating movement in the slot 9 against the spring pressure. At no-load during the operation of the device, the sliding of the cutting edge 4 of the cutter 5 over the shear plate 1 will give rise to small frictional forces which provide a certain damping. If for some reason the cutting edge 4 of the cutter should get out of engagement with the shear plate 1, it will rapidly and undampedly be returned into this engagement by the force of the spring 11. This force exerted by the spring 11 may be of the same order of magnitude as the force exerted on the cutter 5 by gravitation but will exceed it.

In the embodiment shown in FIG. 4 a part of the shank of the cutter 5, which part is situated between the holder 8 and the shear plate 1, is shaped in the form of a hook. Practice has shown that in this embodiment a highly satisfactory constant engagement between the cutter and the shear plate is achieved.

During the cutting action of the device, the forces exerted on the cutter 5 and directed along the axis of the aperture 9 in the holder 8, tend to an equilibrium, while of these forces, those which are directed towards the cutting edge 4 of the cutter 5, will adapt themselves to the forces directed away from this cutting edge 4. I

To illustrate the above, FIG. 5 shows schematically a number of significant forces which occur in an embodiment as shown in FIG. 3 and which act on the cutter 5 during the cutting action of the device, where,

d=the thickness of the holder,

a the spacing between the holder and the shear plate,

F the pressure of the spring.

In an equilibrium situation we have the following equations:

The adaptation of W, and W; to K will be clear from these equations. Furthermore practice has shown that with the use of a shear plate in the form of a perforated foil a very satisfactory engagement of the cutting edges of the cooperating cutters is obtainable.

What is claimed is:

1. In a hair-cutting apparatus such as a dry shaver including a casing and a shear plate with hair-receiving apertures, a cutter-holder driven in a movement generally parallel to the plane of the plate and having an aperture extending generally normal to said holder movement, a cutter having a shank part engaged to and moved by the holder and a blade part that is moved in contact with the shear plate, the shank pan being axially movable and slightly inclinable in said holder aperture; a spring member in the casing urging the cutter blade into contact with the shear plate, the spring having a force only slightly greater than the gravitational force developed by said cutter, the cutter at the commencement of cutting a hair, becoming slight] inclined, at which time the shank part engages axially space portions of the holder where reaction and friction forces develop, that balance forces causing said inclination, with the blade thus restrained from moving further away from the shear plate.

2. In a hair-cutting apparatus such as a dry shaver including a casing, a shear plate with hair-receiving apertures, a cutter having a shank part, and a blade part that is moved in contact with the shear plate, a cutter-holder driven in a movement generally parallel to the plate and having an aperture for receiving and holding the cutter shank part which is axially movable and slightly inclinable therein relative to said cutter holder, a spring member operable with the holder'for urging the cutter such that its blade part is maintained in contact with the shear plate, the spring having a force only slightly greater than the gravitational force developed by said cutter, the cutter at the commencement of cutting a hair, becoming slightly inclined, at which time the shank part clampingly engages the holder where reaction and friction forces develop that balance forces causing said inclination, with the blade thus restrained from moving axially further away from the shear plate.

3. Apparatus according to claim 1 wherein said shear plate is circular and the cutter is driven in a rotary motion.

4. Apparatus according to claim 1 wherein the aperture opening and the shank are prismatic in cross section.

5. Apparatus according to claim 1 wherein the blade portion of the cutter between the holder and shear plate is hookshaped in longitudinal sectional view.

6. Apparatus according to claim 1 wherein the shear plate comprises a perforated foil. 

